A critical examination of three-point bending for determining Young's modulus

The three point bending method is commonly used for determining Young's modulus, E. However, the literature E values of some common pharmaceutical excipients, determined by three point bending, exhibit orders of magnitude variability that cannot be fully explained by normal variations in material properties. To understand the root cause for the large variations, we assessed several potential experimental factors, including instrument stiffness, data analysis method, test speed, alignment between loading beam and specimen surface, and ratio of sample thickness to distance between two supports. Our results show that E value is sensitive to 1) deformation of instrument under force, 2) force-displacement data analysis method, 3) misalignment between loading beam and specimen surface, 4) flashing at the edge of a specimen, 5) accuracy of the true density. Finally, strategies to improve the accuracy of E determination by the three point bending method were recommended.